When a bridge and an elevated highway collapsed during the big San Francisco earthquake of 1989, Minoru Hirano, a Japanese highway designer, reassured his countrymen that Japanese bridges were stronger than those in America.

"I didn't think it would happen to Japan," Mr. Hirano, director of project planning for the Japan Highway Public Corporation, recalled today. "I thought our design code would be enough."

But as a major elevated highway toppled to its side and thousands of buildings crumpled in a huge earthquake near Kobe this morning, Mr. Hirano and others in Japan realized, to their horror, that it could happen here. "We can never be prepared enough. That's my comment now," he said.

The earthquake, which measured 7.2 on the Richter scale, shook more than foundations. It has undermined Japan's confidence in its anti-quake technology and raised the level of fear in a nation that thought it had reached an accommodation with an ever-present threat.

Most prediction efforts are aimed at forecasting a quake southwest of Tokyo, not in western Japan. "We do not have any earthquakes there," said Shin Aoyama, a spokesman for the Science and Technology Agency. "It's really an astonishing event."

The last big earthquake in western Japan was in 1946. Measuring 8.0 on the Richter scale, it killed more than 1,300 people. Lack of preparation in Kobe, a port city, may have contributed to the scope of the devastation.

Many questions remain unanswered. Japanese buildings and homes have systems that automatically shut off the gas in the event of an earthquake. It is still unclear whether these systems were in use near Kobe and, if so, why there were dozens of fires, many of which had still not been extinguished by nightfall.

Some of the houses and office buildings that collapsed might have been built before the earthquake code was revised in the 1970s.

Mr. Hirano of the government-affiliated highway corporation said that, in general, the panels of the roadbed on elevated highways in Japan are connected to each other more firmly together than they are in the United States. The roadbed is also connected more strongly to the pillars.

With one highway that collapsed today, he said, the roadbed stayed intact and connected to the pillars. But the entire structure toppled over as one piece, collapsing at the base of its pillars, perhaps because the ground supporting the pillars gave way.

The other highway that collapsed was the oldest in Japan, opened in 1965, he said. Mr. Hirano said he thought highways in western Japan were not upgraded to the latest standards because the threat of earthquakes there was perceived to be low.

After last year's Los Angeles quake, Hisanobu Ichimasu, director of the design and research division in Tokyo's Metropolitan Expressway Public Corporation, said Japan's and California's standards for elevated roadways were now very similar, although at one time Japan had a more stringent code.

For instance, he said, until a big quake in the San Fernando Valley in 1971, California required fewer horizontal steel hoops in pillars than Japan did. The hoops are designed to prevent the vertical steel reinforcing bars from buckling outward. But now, he said, the standards are similar.

Masakazu Ozaki, a professor of architectural engineering at Chiba University, said that "mostly Japanese buildings are stronger than U.S. buildings," but that it depends on the type of building.

Still, he and others said a revision of Japan's codes will now be inevitable. Professor Ozaki said it is politically difficult in Japan to criticize the building codes because people do not typically challenge the government here.

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Perhaps no place on earth, including California, lives under as constant a threat of earthquakes as Japan. Today's quake was the third since October that measured over 7.0 on the Richter scale.

But most earthquakes in recent years, including the two other big ones since October, have done little damage and resulted in few casualties. Even in a July 1993 earthquake that measured 7.8 on the Richter scale and killed more than 200 people, almost all the deaths and damage resulted from huge tsunami waves rather than from the earth's shaking itself.

The result, some people here say, is that Japan became overconfident and somewhat complacent.

Japan's newspapers and television stations provided extensive coverage of the San Francisco earthquake, which measured 7.1 on the Richter scale, and of the Los Angeles temblor, of 6.7 magnitude, which occurred exactly a year ago. While the media questioned whether the same damage could occur in Japan, experts were frequently quoted saying how Japanese building and highway codes here were more stringent than California's.

To some extent, Japan's ability to withstand earthquakes is probably better than in the United States, experts say. But some of Japan's good track record can also be attributed to luck. Most of the big earthquakes have occurred in the Pacific Ocean or near lightly populated areas.

The epicenter of today's earthquake was very near Kobe and at a relatively shallow depth of 20 kilometers, or 12.4 miles. That makes it the first big temblor to occur in a major city since the great Tokyo earthquake of 1923, in which more than 140,000 people died.

Earth quakes are a major concern for the Japanese. Children are trained to prepare for earthquakes from an early age; some elementary schools require pupils to sit on fireproof seat cushions that can be worn as a hat to shield the head from falling debris. In the 1970's, the Tokyo fire department gave away free to each home a plastic water bucket that would hold enough water for a week's worth of drinking or for dousing fires after a quake.

Every Sept. 1, the anniversary of the great Tokyo earthquake, millions of people in the Tokyo area take part in earthquake drills. Children practice running through tunnels of smoke with handkerchiefs over their faces and military personnel practice rescues from helicopters.

Japan is also spending about $106 million a year to study the mechanism of earthquakes in an effort to eventually be able to predict them.

The government is using signals from satellites and distant stars to measure minute shifts in the earth's crust. It is drilling wells more than a mile deep in which to put equipment to measure earth movements, and it is monitoring faults under the ocean. One project, to see if the behavior of catfish can provide a warning of earthquakes, has drawn some international ridicule.

"The government is always saying that Japanese buildings are completely safe," said Mr. Ozaki, who is the Japanese chairman of a United States-Japan committee looking at how to improve building design to withstand earthquakes.

No matter how the codes are improved, he said, no building will ever by completely free from risk from a big enough earthquake. In that sense, some Japanese are resigned to living with a permanent threat of quakes.

"I have a feeling there's nothing we can do about it," said Yukio Suzuki, an office worker in Tokyo. "Just make sure to turn off the gas. You don't want to worry too much or you become neurotic."

For Kayoko Onishi, 77, today's earthquake revived memories of the 1923 Tokyo quake, which she experienced as a little girl and which killed her father. "We had to sleep outside in our big garden, under a table," she said today. "We couldn't go back inside the house."

Now, she said, she is scared again, but there is little she can do. "This is my country and I can't escape anywhere else," she said.

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A version of this article appears in print on January 18, 1995, on Page A00014 of the National edition with the headline: QUAKE IN JAPAN: THE ENGINEERING; Devastation Shakes Trust In Construction Standards. Order Reprints|Today's Paper|Subscribe